RF receiver system with adjustable impedance matching

Abstract

A RF receiver system for an MRI apparatus includes a receive coil, which exhibits a total effective coil impedance composed of the coil impedance of the coil itself and a patient impedance. An analog-to-digital converter is connected to an amplifier for converting the amplified output signal from the amplifier to a digital signal for further processing. A matching network is interconnected between the receive coil and the amplifier and includes a matching system with an adjustable impedance for matching the total effective coil impedance to the lowest noise impedance, and a noise calculation unit is connected to the analog-to-digital converter for receiving the digital output signal of the converter and is configured to calculate noise of the output signal of the analog-to-digital converter and for adjusting the adjustable impedance of the matching network in order to calibrate the matching network for every patient individually before the scanning process.

The invention claimed is: 
     
       1. A radio frequency receiver system for an MRI apparatus, comprising:
 a receive coil for being attached to a patient which is to be examined by the MRI apparatus and which in such a state in which it is attached to the patient exhibits a total effective coil impedance which is composed of the coil impedance of the coil itself and the patient impedance due to the patient to who the coil is attached, 
 an amplifier which exhibits a lowest noise impedance and which is connected to the receive coil for amplifying a signal received from the receive coil and outputting an amplified output signal, 
 an analog-to-digital converter which is connected to the amplifier for converting the amplified output signal from the amplifier to a digital signal for further processing, 
 a matching network which is interconnected between the receive coil and the amplifier and which comprises a matching system with an adjustable impedance for matching the total effective coil impedance to the lowest noise impedance, the matching network further comprising a capacitive portion with at least one capacitor, or several capacitors, and 
 a noise calculation unit which is connected to the analog-to-digital converter for receiving a digital output signal of the analog-to-digital converter and which is adapted for calculating a noise of the output signal of the analog-to-digital converter, determining the lowest noise and for adjusting the adjustable impedance of the matching network, and wherein the amplifier is integrated with the matching network's capacitive portion and the noise calculation unit. 
 
     
     
       2. The radio frequency receiver system of  claim 1 , wherein the amplifier is a low-noise amplifier. 
     
     
       3. The radio frequency receiver system of  claim 1 , wherein matching network's capacitive portion comprises an adjustable capacitor bank. 
     
     
       4. The radio frequency receiver system of  claim 1 , wherein the capacitor bank is a monolithically integrated capacitor bank. 
     
     
       5. The radio frequency receiver system of  claim 1 , wherein the matching network's capacitive portion, the amplifier and the analog-to-digital converter are integrated on a monolithic die. 
     
     
       6. The radio frequency receiver system of  claim 1 , wherein the matching network further comprises at least one inductor. 
     
     
       7. The radio frequency receiver system of  claim 6 , wherein the at least one capacitor which is separate from the monolithic die has a fixed capacitance. 
     
     
       8. The radio frequency receiver system of  claim 6 , wherein the matching network further comprises a capacitor separate from a monolithic die. 
     
     
       9. A method for operating a radio frequency receiver system for an MRI apparatus, wherein a receive coil exhibits a total effective coil impedance which is composed of the coil impedance of the coil itself and a patient impedance due a patient which is to be examined by the MRI apparatus and with respect to whom the coil is arranged, the method comprising the following method steps:
 receiving a signal from the receive coil by an amplifier which exhibits an impedance-, 
 amplifying the signal received from the receive coil by the amplifier, 
 outputting an amplified output signal from the amplifier to an analog-to-digital converter, 
 converting the amplified output signal from the amplifier to a digital signal for further processing in the analog-to-digital converter, and 
 matching the total effective coil impedance to a lowest noise impedance by a matching network which is interconnected between the receive coil and the amplifier and which comprises a matching system with an adjustable impedance. 
 
     
     
       10. The method of  claim 9 , wherein the method further comprises the method steps of: receiving a digital output signal of the analog-to-digital converter by a noise calculation unit, and calculating a noise of the output signal of the analog-to-digital converter. 
     
     
       11. The method of  claim 9 , wherein the method further comprises the method step of: adjusting the adjustable impedance by varying a ratio between a first adjustable impedance of a first capacitor and a second adjustable impedance of a second capacitor. 
     
     
       12. The method of  claim 9 , wherein the adjusting of the adjustable impedance is controlled automatically. 
     
     
       13. A non-transitory computer-readable medium, comprising instructions stored thereon, that when executed on a processor induce a radio frequency receiver system for an MRI apparatus to perform a method according to  claim 9 .